Hands-free system and method for opening trunk

A hands-free system and method for opening a trunk, that include a trunk antenna 100 and a smart key 200 that transmits a sensing response signal or an authentication response signal, when receiving a sensing signal or an authentication signal from the trunk antenna 100. In addition, the smart key receives and stores a hands-free function setting and transmits the sensing response signal with function setting information when the hands-free function is set. Further, a receiving antenna 300 receives a sensing response signal or an authentication response signal from the smart key 200. A controller 400 transmits an authentication signal when the trunk antenna 100 transmits a sensing signal during a predetermined period and the receiving antenna 300 receives a sensing response signal that includes function setting information a predetermined number of times. The controller 400 performs authentication when the receiving antenna 300 receives an authentication response signal and outputs a trunk opening signal when the authentication is allowed.